Washing agent and a process for washing acidic components from a gas stream

ABSTRACT

THE WASHING AGENT INCLUDES A CARBOXYLIC ACID AMIDE OF MORPHOLINE PREFERABLY CONTAINING BETWEEN 1 AND 7 CARBON ATOMS IN THE CARBOXYLIC ACID CHAIN. THE GASEOUS ACIDIC COMPONENTS ARE ABSORBED BY THE CARBOXYLIC ACID AMIMDE OF MORPHOLINE AND MAY BE REMOVED THEREFROM BY DISTILLATION AT ABOUT 80*C. THE PROCESS FOR WASHING THE GASEOUS ACIDIC COMPONENTS SUCH AS CARBON DIOXIDE, HYDROGEN SULFIDE AND HYDROGENCYANIDE FROM A GAS STREAM INCLUDES TREATING THE GAS STREAM WITH A WASHING AGENT THAT ABSORBS AT LEAST A PORTION OF THE GASEOUS ACIDIC COMPONENTS. THE WASHING AGENT INCLUDES ONE OR MORE CARBOXYLIC ACID AMIDES OF MORPHOLINE IN A DILUTED OR UNDILUTED FORM. THE GASEOUS ACIDIC COMPONENTS ARE ABSORBED BY THE CARBOXYLIC ACID AMIDES OF MORPHOLINE AND CAN BE REMOVED THEREFROM BY DISTILLATION AT RELATIVELY LOW TEMPERATURES. THE CARBOXYLIC ACID AMIDES OF MORPHOLINE SELECTIVELY ABSORB BETWEEN 7 AND 8 VOLUMES OF HYDROGEN SULFIDE FOR EACH VOLUME OF CARBON MONOXIDE ABSORVE FROM THE GAS STREAM.

3,773,896 WASHING AGENT AND A PROCESS FOR WASH- ING AClDIC COMPONENTS FROM A GAS STREAM Gerhard Preusser, Essen, and Martin Schulze, Neviges, Germany, assignors to Heinrich Koppers Gesellschaft mit beschrankter Haftung, Essen, Germany No Drawing. Filed Apr. 26, 1971, Ser. No. 137,594 Int. Cl. B01d 53/34 U.S. Cl. 423-226 5 Claims ABSTRACT OF THE DISCLOSURE The washing agent includes a carboxylic acid amide of morpholine preferably containing between 1 and 7 carbon atoms in the carboxylic acid chain. The gaseous acidic components are absorbed by the carboxylic acid amide of morpholine and may be removed therefrom by distillation at about 80 C. The process for washing the gaseous acidic components such as carbon dioxide, hydrogen sulfide and hydrogen cyanide from a gas stream includes treating the gas stream with a washing agent that absorbs at least a portion of the gaseous acidic components. The washing agent includes one or more carboxylic acid amides of morpholine in a diluted or undiluted form. The gaseous acidic components are absorbed by the carboxylic acid amides of morpholine and can be removed therefrom by distillation at relatively low temperatures. The carboxylic acid amides of morpholine selectively absorb between 7 and 8 volumes of hydrogen sulfide for each volume of carbon monoxide absorbed from the gas stream.

BACKGROUND OF THE INVENTION (1) Field of the invention This invention relates to a washing agent for removing acidic components from a gas stream and more particularly to a washing agent and process for removing acidic components from a gas stream by absorbing the gaseous acidic components in a washing agent that includes one or more carboxylic acid amides of morpholine.

(2) Description of the prior art Washing acidic gaseous components from a gas stream with a suitable washing agent and thereafter regenerating the washing agent by removing the acidic components from the washing agent by heating is well known. Aqueous solutions of strong organic bases and alkali metal salts of weak organic or inorganic acids have been used extensively as washing agents. Amines such as ethanolamines are well known examples of such washing agents. These washing agents form a chemical bond with the gaseous acidic components that are removed from the gas stream and are therefore known as chemically acting washing agents. The removal of the gaseous acidic components is the result of a chemical reaction between the gaseous acidic component and the washing agent.

Problems have been encountered in the past with the use of chemically active washing agents. The chemical bond formed during the washing process between the washing agent and the gaseous acidic components must be broken to bring about removal of the gaseous acidic components from the washing agent. A substantial amount of thermal energy is required to break this chemical bond and effect a separation of the acidic components from the washing agent.

Belgian Pat. 726,081 suggests the use of both pure and C-substituted morpholines as washing agents. C-substituted or pure morpholines, however, are strong bases that are believed to undergo acid base reactions and form compounds with the gaseous acidic components that are United States Patent 0 removed from the gas stream. The bonds of these compounds must also be broken to regenerate the washing :gent and remove the gaseous acidic components thererom.

US. Pat. 3,434,936 suggests the use of an N-substituted morpholine for extractive distillation of aromatic compounds from hydrocarbon mixtures containing the same.

SUMMARY OF THE INVENTION The hereinafter described invention is directed to a washing agent for absorbing gaseous acidic components from a gas stream. The gaseous acidic components of the gas stream include gaseous acidic components such as CO H S and HCN, and particularly gaseous acidic components that are absorbed by carboxylic acid amides of morpholine.

The washing agent includes a carboxylic acid amide of morpholine and preferably one which contains 1 through 7 carbon atoms in the carboxylic acid group. The process for washing the gaseous acidic components from the gas stream includes passing the gas stream containing the gaseous acidic components through a washing agent comprising a carboxylic acid amide of morpholine and absorbing at least a portion of the gaseous acidic components by the carboxylic acid amide of morpholine. The carboxylic acid amide of morpholine in the washing agent is regenerated by subjecting the carboxylic acid amide of morpholine to an elevated temperature of about C. where at least a portion of the gaseous acidic components are evolved from the carboxylic acid amide of morpholine and the carboxylic acid amide of morpholine is suitable for reuse in the washing agent. Where the gaseous acidic components include carbon dioxide and hydrogen sulfide and the carboxylic acid amides of morpholine in the washing agent contain between 1 and 7 carbon atoms in the carboxylic acid group, the carboxylic acid amide of morpholine selectively absorbs between about 7 and 8 volumes of hydrogen sulfide for each volume of carbon dioxide. Also, where the gaseous acidic components contain carbon monoxide and hydrogen sulfide and the carboxylic acid amides of morpholine contain between 1 and 7 carbon atoms in the carboxylic acid group, between 70 and 80 percent of the hydrogen sulfide absorbed by the carboxylic acid amide of morpholine and between 55 and 65 percent of the carbon monoxide absorbed by the carboxylic acid amide of morpholine is evolved therefrom when the carboxylic acid amide of morpholine is subjected to an elevated temperature of about 80 C.

The carboxylic acid amides of morpholine have a distinctive weakly basic character in contrast to the strongly basic character exhibited by known Washing agents. It has been found that the carboxylic acid amines of morpholine with from 1 to 7 carbon atoms in the carboxylic acid group have a strong ability to absorb gaseous acidic components in spite of their weakly basic character. It is believed that the dissolution by such amides of the gaseous acidic components is due to a physical absorption as contrasted with the formation of an intermediate chemical compound by chemical reaction. Separation of the acidic components from the washing agent is easily accomplished by low temperature distillation with less thermal energy being required as compared with the thermal energy previously used with chemically acting washing media.

It has also been discovered that the carboxylic acid amides of morpholine have a marked preference for the absorption of hydrogen sulfide over other gaseous acidic components in the gas stream. This feature contributes substantially to the selective removal of hydrogen sulfide from a gas stream containing several gaseous impurities.

Thus the two major deficiencies in the known processes of washing a gas stream to remove gaseous acidic components therefrom have been eliminated by the hereinafter disclosed washing agent containing carboxylic acid amides of morpholine.

It is therefore a principal object of this invention to provide an improved washing agent for removing gaseous acidic components from a gas stream that is easily able to be regenerated for further use.

Another object of this invention is to provide a washing agent with improved selectivity for hydrogen sulfide present as one of several gaseous acidic components.

These and other objects and advantages of this invention will be more completely disclosed and described in the following specification and the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A component of the hereinafter described washing agent is selected from the class of carboxylic acid amides of morpholine preferably having between 1 and 7 carbon atoms in the carboxylic acid group. Typical of such a compound is N-formyl morpholine or N-acetyl morpholine. The carboxylic acid amine of morpholine component may be used in a washing agent that is prepared as either a diluted solution or an undiluted solution. When the washing agent is prepared in diluted form either Water or an organic solvent such as an alcohol may be used as the diluent. An undiluted carboxylic acid amide may also be employed as a washing agent where the presence of a solvent would adversely affect the washing process. The washing agent may also be prepared as a mixture of a carboxylic acid amide or amides and chemically acting washing agents such as amines. Mixtures consisting of two or more carboxylic acid amides or mixtures of carboxylic acid amides with other carbon substituted or nitrogen substituted morpholines are also effective as washing agents.

The absorption of the gaseous acidic components by the liquid washing agent may take place in any one of several kinds of apparatus specifically designed for an absorption process. Generally, equipment for gas absorption is designed to bring the gas and liquid components into intimate mutual contact to give maximum transfer of the gaseous components into the liquid. The gas stream to be Washed may be bubbled through the liquid washing agent by means of a number of perforated gas pipes laid in the bottom of a tank containing the liquid. A closed chamber containing the gas to be washed may be sprayed with jets of liquid under high pressure which absorb certain gaseous components.

The equipment most generally employed for gas'absorption is a contacting tower consisting of a cylindrical vessel with gas inlets at the bottom and liquid inlets at the top. The vessel is preferably filled with a suitable inert solid packing material that provides a large surface area within the tower over which the liquid flows, forming a film that provides a relatively large liquid surface area for contact with the gas stream that moves upwardly through the tower.

The washing agent, enriched by the absorbed acidic gaseous components, may be regenerated for return to the washing tower by removal of the acidic components. The removal of the acidic components may take place at normal pressures or at increased pressures by any of the known methods as, for example, stripping with an inert gas or by distillation at relatively low temperatures. The herein described washing agent may be easily regenerated by distillation at a temperature of about 80 C. Since the boiling point of the carboxylic acid amides of morpholine is in the region of 128 0., low temperature distillations that vaporize the gaseous acidic components without a phase change in the washing agent may be employed. The regenerated washing agent may thereafter be cooled and recycled through the washing process.

The table illustrates the experimental results obtained by treating a gas stream containing carbon dioxide and hydrogen sulfide as the gaseous acidic component. Separation Runs 1 and 2 where performed for comparative reasons and used the previously known chemically active washing agents. Runs 3 through 9 used washing agents that included carboxylic acid amides of morpholine either alone or in mixtures. The absorptive power of the washing agents expressed in Bunsen coefficients for both carbon dioxide and hydrogen sulfide were compared. It is apparent from the table that runs 3 through 9 illustrate the superior absorptive power of the carboxylic acid amides of morpholine, particularly runs 3 through 7 where the carboxylic acid amides of morpholine contained between 1 and 7 carbon atoms in the carboxylic acid group.

The selectivity of the washing agents were also determined and is expressed as a ratio of the hydrogen sulfide and carbon monoxide gas removed from the gas stream. It will be apparent from the comparative selectivity that the carboxylic acid amides of morpholine, particularly those containing between 1 and 7 carbon atoms in the carboxylic acid chain, where substantially superior to that of the chemically active washing agents of runs 1 and 2. For example, the N-acetyl morpholine of run 4 absorbed 8.5 times the hydrogen sulfide than the carbon dioxide.

The ability to separate or remove the absorbed carbon dioxide and hydrogen sulfide from the washing agent was also determined. It will be apparent from the table that it is now possible to effectively separate the absorbed gaseous acidic components from the washing agent by distillation at a temperature of about 80 C. when the washing agent is a carboxylic acid amide of morpholine.

The results disclosed in the table clearly illustrate the superiority of the carboxylic acid amides of morpholine with from 1 to 7 carbon atoms in the carboxylic group as washing agents both in selectively removing H 8 and separating the absorbed acidic components from the carboxylic acid amides of morpholine.

According to the provisions of the patent statutes we have explained the principle, preferred embodiments and mode of operation of our invention and have described what we consider to represent its best embodiments. However, it should be understood that within the scope of the appended claims, the invention may be practiced otherwise than as epecifically described.

Separation by distillation up to 80 C. in percent Gas absorptive power in bunsen absorption of the absorption coefiicients Selectivity: gas

absorption Hrs/gas Run No; Washing media 00, H 8 absoprtion C0 C01 H 8 Propylene carbonate 3.6 13.2 3.7 56 64 Suit 1 2.5 14.5 5.8 84 72 3. 6 26. 2 7.3 63 79 3.4 28.9 8. 6 59 74 3. 2 26. 0 8. 1 58 80 3.2 23. 2 7.3 65 2. 5 26. 5 7. 6 65 78 3.2 15. 6 4. 9 69 72 2. 7 20. 9 7. 7 75 69 5 We claim: 1. A process for washing gaseous acidic components from a gas stream comprising passing a gas stream containing one or more gaseous acidic components selected from the group consisting of H 8, C0 and HCN and mixtures thereof through a washing agent comprising a carboxylic acid amide of morpholine containing between 1 and '7 carbon atoms in the carboxylic acid chain, and absorbing at least a portion of said gaseous acidic components in said gas stream by said carboxylic acid amide of morpholine. 2. A process for washing gaseous acidic components from a gas stream as set forth in claim 1 which includes subjecting said washing agent containing gaseous acidic components absorbed by said carboxylic acid amide or morpholine to an elevated temperature of about 80 C. to separate at least a portion of said gaseous acidic components from said carboxylic amide of morpholine. 3. A process for washing gaseous acidic components from a gas stream as set forth in claim 1 in which said gaseous acidic components include CO and H 5,

and selectively absorbing between about 7 and 8 parts of 6 H 8 for each volume of CO by said carboxylic acid amide of morpholine in said washing agent. 4. A process for washing gaseous acidic components from a gas stream as set forth in claim 2 in which said gaseous acidic components include CO and H 8,

and separating between 70 to 80 percent of the H 8 absorbed by said carboxylic acid amide of morpholine. 5. A process for washing gaseous acidic components 10 from a gas stream as set forth in claim 4 which includes separating between about 55 and 65 percent of the CO absorbed by said carboxylic acid amide of morpholine.

References Cited UNITED STATES PATENTS 3,555,782 1/1971 Deringer 55-73 3,417,114 12/1968 Kuceski 260247.7 H 3,558,619 1/1971 'Hofimann et al. 260247.7 H

EARL c. THOMAS, Primary Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE Patent: No.

November 20, 1973- Inventor(s) Dated Gerhard Preusser and Martin Schulze It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In The Table Column 3, Line 14 Under CO Signed and sealed this 6th day of August 1974.

(SEAL) Attest:

MCCOY M. GIBSON, JR. Attesting Officer "where" should read '--were-- I "were" should. read "where" should read- "'epecifioally should read --specifically-' "mixtures" shouldread -'--mixture'- "2.5" should read c. MARSHALL DANN Commissioner of Patents 

